Pore‐Filling of Spiro‐OMeTAD in Solid‐State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device Performance

Ding, I‐Kang; Tétreault, Nicolas; Brillet, Jérémie; Hardin, Brian E.; Smith, Eva H.; Rosenthal, Samuel; Sauvage, Frédéric; Grätzel, Michaël; McGehee, Michael D.

doi:10.1002/adfm.200900541

Cited by 257 publications

(290 citation statements)

References 31 publications

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“…The effects of such nanoscale confinement on molecular mobility are attracting increasing interest for applications such as pore filling in solid-state dye-sensitized solar cells 7 and molecular sieving in nanofilters. 8 However, there is a remarkable paucity of molecular mobility data under nanoconfinement, and fundamental descriptions are complicated not only by the effects of the confinement on molecular interactions, conformation, and free volume but also by molecular interactions with the confining surfaces.…”

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confidence: 99%

Molecular Mobility under Nanometer Scale Confinement

Kim

Dauskardt

2010

Nano Lett.

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The mobility of organic molecules under nanoscale confinement differs greatly from that in the bulk. In this study we show that the conventional free volume dependent mobility relationship explained by the free volume theory of diffusion breaks down for diffusion of linear alkane molecules in organosilicate films with connected nanoporosity. Alkane mobility under such nanoscale confinement was observed to decrease with chain length and was lower than that reported in the bulk. While the activation energy for diffusion was similar to that in the bulk, it was found to decrease with chain length exactly opposite to the trend observed in the bulk. This suggests an increasing molecular free volume with chain length. The effects of molecular polarity and pore size on diffusion were also demonstrated. Molecular mobility was found to be suppressed with increasing molecular polarity and decreasing pore size. KEYWORDS Molecular mobility, nanoporous, nanoconfinementT he mobility of organic molecules when confined at nanometer length scales differs greatly from properties in the bulk. 1,2 We demonstrate that linear alkane molecules exhibit a free volume dependent mobility under nanoconfinement that is exactly opposite to the conventional relationship observed in the bulk. As described by the free volume theory of diffusion, 3-5 linear alkane molecules typically exhibit a lower free volume and mobility with longer chain lengths. 6 However, under nanoscale confinement in nanoporous organosilicate films, we found the activation energy decreases with increasing chain length suggesting an increase in the molecular free volume.The effects of such nanoscale confinement on molecular mobility are attracting increasing interest for applications such as pore filling in solid-state dye-sensitized solar cells 7 and molecular sieving in nanofilters. 8 However, there is a remarkable paucity of molecular mobility data under nanoconfinement, and fundamental descriptions are complicated not only by the effects of the confinement on molecular interactions, conformation, and free volume but also by molecular interactions with the confining surfaces. We recently showed that unentangled surfactant molecules in the bulk become entangled with adjacent molecules when diffusing through interconnected nanopores (d ∼ 2.1 nm) and exhibit signatures of reptation. 9 We also discussed the importance of molecular interactions with pore surfaces. Other studies have shown that long polystyrene molecules with molecular weight above that needed for entanglement diffuse faster in cylindrical alumina nanopores (pore diameter d ∼ 15 nm) due to lower molecular entanglement associated with fewer chains present in the confined region. 10 According to the free volume theory of diffusion, 3-5 the two ends of a linear chain molecule provide a contribution to free volume into which segments of adjacent molecules can move. The fractional free volume, f, provided by the chain ends is inversely proportional to the chain length or the molecular weight, M, and incre...

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confidence: 99%

Molecular Mobility under Nanometer Scale Confinement

Kim

Dauskardt

2010

Nano Lett.

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“…10 Currently, the best performing ss-DSCs achieve power conversion efficiencies of up to 7.2%, 11 thus still lagging behind DSCs based on a liquid electrolyte, which are now over 12%. 12 The underperformance of ss-DSC is thought to be associated with three main challenges: (i) limited pore-filling of the mesoporous TiO 2 with the HTM to ensure the optimum composition of the photo-active layer, [13][14][15][16] (ii) panchromatic absorption of light, which is currently limited by the maximal film thickness of well-performing ss-DSCs, 17 and (iii) efficient charge generation and transport from the excited dye to maximize the current output from the sunlight. [18][19][20][21][22][23][24][25] While issues with efficient charge generation have been extensively addressed (though not resolved) in earlier work, [18][19][20][21][22][23][24] the related challenges of effective pore-filling and sufficient panchromatic absorption remains open.…”

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Pore Filling of Spiro‐OMeTAD in Solid‐State Dye‐Sensitized Solar Cells Determined Via Optical Reflectometry

Docampo

Hey

Guldin

et al. 2012

Adv Funct Materials

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Here, we present an optical probe to determine the pore-filling fraction of the hole-conductor 2,2-7,7-tetrakis-N,N-di-pmethoxyphenylamine-9,9-spirobifluorene (spiro-OMeTAD) into mesoporous photoanodes in solid-state dye-sensitized solar cells (ss-DSCs). Based on refractive index determination by the film's reflectance spectra, and using effective medium approximations, we can extract the volume fractions of the constituent materials and hence quantify pore-filling. This non-destructive method can be used with complete films and does not require detailed model assumptions.pore-filling fractions of up to 80% were estimated for optimized solid-state DSC photoanodes, which is higher than that previously estimated by indirect methods.Additionally, we have determined transport and recombination lifetimes as a function of the pore-filling fraction via photovoltage and photocurrent decay measurements. While extended electron lifetimes were observed with increasing pore-filling fractions, no trend was found in the transport kinetics. The data suggests that a pore-filling fraction of at least 60% is necessary to achieve optimized performance in ss-DSCs. This degree of pore-filling is even achieved in 5 µm thick mesoporous photoanodes. We can therefore conclude from this study that pore-filling is not a limiting factor in the fabrication of thick ss-DSCs.

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“…Hence, solidification of electrolyte is one of important techniques to improve these problems. Recently, several materials, such as CuSCN [3], 2,2',7,7'-tetrakis (N,N'-di(4-methoxyphenyl)-amine)-9,9'-spirobifluorene (spiro-OMeTAD) [4], polyvinylidene difluoride (PVDF) [5], have been developed as a potential candidate of the solid-state electrolyte.…”

Section: Introductionmentioning

confidence: 99%

Dye-sensitized solar cells using an anion-conducting polymer as a material of solid-state electrolyte

Ota

Hyodo

Shimizu

et al. 2012

2012 International Conference on Renewable Energy Research and Applications (ICRERA)

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Abstract-An anion-conducting polymer (ACP) has been used as an electrolyte material of solid-state dye-sensitized solar cells (DSCs) and the basic electrochemical properties of DSCs have been examined in this study. Initial photocurrent-voltage characteristics of the DSC prepared with ACP (DSC-S) were inferior to those of the DSC prepared with a general liquid electrolyte (DSC-Liq), but DSC-S exhibited better long-term stability. From AC impedance measurements, the relatively poor photocurrent-voltage characteristics of the as-fabricated DSC-S were anticipated to arise from larger resistance of charge transfer at electrolyte/TiO 2 electrode interface than that of the as-fabricated DSC-Liq.

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Pore‐Filling of Spiro‐OMeTAD in Solid‐State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device Performance

Cited by 257 publications

References 31 publications

Molecular Mobility under Nanometer Scale Confinement

Molecular Mobility under Nanometer Scale Confinement

Pore Filling of Spiro‐OMeTAD in Solid‐State Dye‐Sensitized Solar Cells Determined Via Optical Reflectometry

Dye-sensitized solar cells using an anion-conducting polymer as a material of solid-state electrolyte

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